1. Air under pressure is forced into the treating cylinder,
which contains the charge of wood. The air penetrates
some species easily, requiring but a few minutes application of pressure. In treating the more resistant species,
common practice is to maintain air pressure from
1/2 to 1 h before admitting the preservative, but the
necessity for lengthy air-pressure periods does not seem
fully established. The air pressures employed generally
range from 172 to 689 kPa (25 to 100 lb /in2), depending on the net retention of preservative desired and the resistance of the wood.